How to load 2 objects in 2 gltf files with a shared material?

I have 2 dungeon scene objects, each exported from blender, each in their own gltf file:

pillar.gltf
pillar.bin
wall.gltf
wall.bin

Both pillar and wall use the same material ‘light grey’ in blender.

Examining the .gltf files, each contains identical materials information:

"materials" : [
        {
            "doubleSided" : true,
            "name" : "grey light",
            "pbrMetallicRoughness" : {
                "baseColorFactor" : [
                    0.3010401427745819,
                    0.3010401427745819,
                    0.3010401427745819,
                    1
                ],
                "metallicFactor" : 0,
                "roughnessFactor" : 0.5
            }
        }
    ],

Is there some way to only transport this information once over the network? In this case, it’s only a few bytes but I’m supposing that with more complicated materials, that would grow. Plus I have more than just these two objects that use ‘light grey’. I want to keep the wall and pillar in distinct files and just get them as and if required.

I tried exporting from blender with the gltf export option Materials=‘placeholder’. Doing that, I see no material reference in the .gltf files at all although I don’t know how to examine the .bin files.